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## How Many People Does It Take To Colonize Another Star System?392

Hugh Pickens DOT Com writes: "The nearest star systems — such as our nearest neighbor, Proxima Centauri, which is 4.2 light-years from home — are so far away, reaching them would require a generational starship. Entire generations of people would be born, live, and die before the ship reached its destination. This brings up the question of how many people you need to send on a hypothetical interstellar mission to sustain sufficient genetic diversity. Anthropologist Cameron Smith has calculated how many people would be required to maintain genetic diversity and secure the success of the endeavor. William Gardner-O'Kearney helped Smith build the MATLAB simulations to calculate how many different scenarios would play out during interstellar travel and ran some simulations specially to show why the success of an interstellar mission depends crucially on the starting population size. Gardner-O'Kearny calculated each population's possible trajectory over 300 years, or 30 generations. Because there are a lot of random variables to consider, he calculated the trajectory of each population 10 times, then averaged the results.

A population of 150 people, proposed by John Moore in 2002, is not nearly high enough to maintain genetic variation. Over many generations, inbreeding leads to the loss of more than 80 percent of the original diversity found within the hypothetical gene. A population of 500 people would not be sufficient either, Smith says. "Five hundred people picked at random today from the human population would not probably represent all of human genetic diversity . . . If you're going to seed a planet for its entire future, you want to have as much genetic diversity as possible, because that diversity is your insurance policy for adaptation to new conditions." A starting population of 40,000 people maintains 100 percent of its variation, while the 10,000-person scenario stays relatively stable too. So, Smith concludes that a number between 10,000 and 40,000 is a pretty safe bet when it comes to preserving genetic variation. Luckily, tens of thousands of pioneers wouldn't have to be housed all in one starship. Spreading people out among multiple ships also spreads out the risk. Modular ships could dock together for trade and social gatherings, but travel separately so that disaster for one wouldn't spell disaster for all. 'With 10,000,' Smith says, 'you can set off with good amount of human genetic diversity, survive even a bad disease sweep, and arrive in numbers, perhaps, and diversity sufficient to make a good go at Humanity 2.0.'"
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## How Many People Does It Take To Colonize Another Star System?

• #### Sure, but... (Score:5, Insightful)

on Friday April 04, 2014 @02:28PM (#46663147) Homepage

By the time we have the tech to build a starship we can just ship out as many embryos as we can fit in a freezer. Job done.

• #### Why send people? (Score:5, Insightful)

on Friday April 04, 2014 @02:29PM (#46663157)
How about a smaller sample of people and a large sperm and egg bank instead?
• #### Maintaining diversity is not the goal (Score:5, Insightful)

on Friday April 04, 2014 @02:38PM (#46663265)

Five hundred people picked at random today from the human population would not probably represent all of human genetic diversity . . . If you're going to seed a planet for its entire future, you want to have as much genetic diversity as possible, because that diversity is your insurance policy for adaptation to new conditions

when it comes to preserving genetic variation

Except that's not the goal.
If you're talking about colonizing another star system (presumably this is way the fuck after we colonize mars, the moon, IO, Titan, Venus, Murcury, and whatever else we feel like) then little things like genetic diversity upon reaching the target are of little concern.

No, you care about GETTING THERE with enough wits about you that you can continue to function, and set up something to expand your capabilities.
The fight is not to keep the diversity we see on earth circa 2000, but rather the fight is against inbreeding from making everyone retarded to the point where they can no longer function.

Once you get there, and establish colonies, food supply, and your ecosphere can expand past the mothership, you can breed like rabbits and let nature take it's course to overcome whatever detrimental effects that being cooped up in a closed space for 30 generations might have had.

Or every generation could be a fucking clone while on the way there. Seriously, this is colonizing ANOTHER SOLAR SYSTEM. This is WAY OUT THERE. It's science fiction. Just what the hell were you planning of propelling this ship with for 30 years?

Hell, taking the long view, just spreading ANY form of sustainable life is a viable goal for this sort of project. At this scale, "humans" are transient things.

• #### Re:Why send people? (Score:5, Insightful)

<slashdot-2016q1@virtual-estates.net> on Friday April 04, 2014 @02:49PM (#46663403) Homepage Journal

No need to raise them all at the same time. The discussion is not about people needed to get the colony going from the start — it is about preserving the genetic diversity over generations.

• #### Re:Sure, but... (Score:3, Insightful)

on Friday April 04, 2014 @02:50PM (#46663409) Journal
Try and focus here, we're talking about the need for genetic diversity.
• #### Re:Absurdly unnecessary (Score:1, Insightful)

on Friday April 04, 2014 @02:53PM (#46663449) Journal
Unhappy thinkers with TMJ can never see the benefits of mouth-breathers.

Once you think you're smart enough to know what traits are desirable, nature will soon teach you how much of a dumb shit you are.

• #### Their poor offspring (Score:3, Insightful)

on Friday April 04, 2014 @02:53PM (#46663453)

While you would clearly be getting volunteers for the start of this task, there is an ethical dillema as far as future generations. Just because parents / grandparents / great-grandparents were totally OK living their entire lives in what would be a fairly finite space, it doesn't mean some members of a future generation wouldn't consider it torture. I guess it might be hard for me to see things from their eyes since they would be born into it, but I'm thinking that after I got to learn some history and see some videos / pictures of Earth, I'd be pretty unhappy stuck on a spaceship forever. I wonder how many would refuse to breed and do the same to their offspring (which would screw up the "diversity", or decide to turn back, or just go stark-raving-mad and murder someone or everyone (destroy the ship), and then your genetic diversity is REALLY screwed.

on Friday April 04, 2014 @03:10PM (#46663663) Homepage Journal

How many people does it take to colonize this star system? Apparently more than the 6 Billion we have on Earth, since we haven't even bothered to get off this damn rock.

Send people to Mars first, then worry about Alpha Centauri (which is a terrible place to send people to anyway. The only thing there is a backwaters galactic planning council office)

--Joe

• #### Meat Bags In Space == Impractical (Score:4, Insightful)

on Friday April 04, 2014 @03:53PM (#46664251) Homepage

Sending meat bags into space is not very practical at all. It's more likely that we'll develop nano-factories and the capability of offloading intelligence into machines. Then we can just create intelligent space drones that replicate themselves as they go along and thus populate the galaxy.

This is actually one of the reasons why some think there is no extraterrestial life advanced enough to pull this off, as we would have noticed it by now. The reasoning behind this is that any society that has such capabilities more than likely destroyed itself before being able to reach this state. Of course, we might just be the first in our universe to pull this off, but don't count on it.

• #### Re:Sure, but... (Score:4, Insightful)

on Friday April 04, 2014 @03:59PM (#46664335)

No method of space travel that seems remotely feasible would dent an overpopulation problem. Suppose we wanted to reduce population growth by 0.1%/year by shipping people out; that's 7 million people per year, something like twenty thousand a day, or one every four or five seconds. Unless we develop something like cheap and practical teleportation over interstellar distances, this isn't going to happen. With any reasonably imaginable tech, it's going to be really expensive to get them into Earth orbit.

We're going to explore the Galaxy because it's out there, to learn things, and to make it much harder for the species to be destroyed.

• #### Re:Sure, but... (Score:4, Insightful)

on Friday April 04, 2014 @04:53PM (#46664883)

Humans are interesting animals.
We are still 80% dependent on fossil fuels for our energy needs and have no clue what we could use at this scale when they're depleted.
But let's worry about what could happen to the sun in 5 billion years!

• #### Re:Sure, but... (Score:4, Insightful)

on Friday April 04, 2014 @05:41PM (#46665209)

The sad thing continues to be postings how staying safe, playing video games, and watching football games continues to be more "fulfilling" than the real adventure you describe. /sigh

One problem is that society has become increasingly risk adverse in many ways - I doubt the Apollo program would pass a NASA safety review today. And we waste billions of dollars to ostensibly prevent a terrorist attack against an airliner, yet we have no problem facing a far higher risk of dying when we drive to the airport.

• #### Re:Sure, but... (Score:5, Insightful)

on Friday April 04, 2014 @06:47PM (#46665683)

... just synthesize the DNA strand and splice it into the appropriate chromosome.

Are we anywhere near that kind of technology yet?

Yes, we can synthesize DNA, and insert it into genomes. We also have terabyte SD cards. They are expensive, but the cost should drop by the time the multi-generational starships are ready to launch.

The human genome has about 4 billion base pairs. Each pair can be encoded in two bits (there are four different monomers). Since each eight bit byte can encode four base pairs, the entire human genome can fit in one GB. But each for each additional genome, we only need to encode the diffs. Humans are 99.9% the same [wikipedia.org] so a typical diff would be about 0.1% of 1GB, or 1MB. But even that understates the compression possible, because that 0.1% is not random. People tend to diverge from other people in "chunks" that are shared across many other people. So a typical person's genome could probably be stored in about 100KB. Properly compressed, a terabyte SD card could contain the genomes of ten million people.

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